/**
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
    *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.apache.hadoop.hbase.replication.regionserver;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.regionserver.wal.ProtobufLogReader;
  import org.apache.hadoop.hbase.wal.WAL.Reader;
  import org.apache.hadoop.hbase.wal.WAL.Entry;
  import org.apache.hadoop.hbase.wal.WALFactory;
  
  import java.io.IOException;
  
  /**
   * Wrapper class around WAL to help manage the implementation details
   * such as compression.
   */
  @InterfaceAudience.Private
  public class ReplicationWALReaderManager {
  
    private static final Log LOG = LogFactory.getLog(ReplicationWALReaderManager.class);
    private final FileSystem fs;
    private final Configuration conf;
    private long position = 0;
    private Reader reader;
    private Path lastPath;
  
    /**
     * Creates the helper but doesn't open any file
     * Use setInitialPosition after using the constructor if some content needs to be skipped
     * @param fs
     * @param conf
     */
    public ReplicationWALReaderManager(FileSystem fs, Configuration conf) {
      this.fs = fs;
      this.conf = conf;
    }
  
    /**
     * Opens the file at the current position
     * @param path
     * @return an WAL reader.
     * @throws IOException
     */
    public Reader openReader(Path path) throws IOException {
      // Detect if this is a new file, if so get a new reader else
      // reset the current reader so that we see the new data
      if (this.reader == null || !this.lastPath.equals(path)) {
        this.closeReader();
        this.reader = WALFactory.createReader(this.fs, path, this.conf);
        this.lastPath = path;
      } else {
        try {
          this.reader.reset();
        } catch (NullPointerException npe) {
          throw new IOException("NPE resetting reader, likely HDFS-4380", npe);
        }
      }
      return this.reader;
    }
  
    /**
     * Get the next entry, returned and also added in the array
     * @return a new entry or null
     * @throws IOException
     */
    public Entry readNextAndSetPosition() throws IOException {
      Entry entry = this.reader.next();
      // Store the position so that in the future the reader can start
      // reading from here. If the above call to next() throws an
      // exception, the position won't be changed and retry will happen
      // from the last known good position
      this.position = this.reader.getPosition();
      // We need to set the CC to null else it will be compressed when sent to the sink
      if (entry != null) {
        entry.setCompressionContext(null);
      }
      return entry;
    }
 
   /**
    * Advance the reader to the current position
    * @throws IOException
    */
   public void seek() throws IOException {
     if (this.position != 0) {
       this.reader.seek(this.position);
     }
   }
 
   /**
    * Get the position that we stopped reading at
    * @return current position, cannot be negative
    */
   public long getPosition() {
     return this.position;
   }
 
   public void setPosition(long pos) {
     this.position = pos;
   }
 
   public long currentTrailerSize() {
     long size = -1L;
     if (reader instanceof ProtobufLogReader) {
       final ProtobufLogReader pblr = (ProtobufLogReader)reader;
       size = pblr.trailerSize();
     }
     return size;
   }
 
   /**
    * Close the current reader
    * @throws IOException
    */
   public void closeReader() throws IOException {
     if (this.reader != null) {
       this.reader.close();
       this.reader = null;
     }
   }
 
   /**
    * Tell the helper to reset internal state
    */
   void finishCurrentFile() {
     this.position = 0;
     try {
       this.closeReader();
     } catch (IOException e) {
       LOG.warn("Unable to close reader", e);
     }
   }
 
 }